During the lifetime of a patient, it may be necessary to perform a total shoulder replacement procedure on the patient as a result of, for example, disease or trauma. In a total shoulder replacement procedure, a humeral component having a prosthetic head is used to replace the natural head of the patient's humerus. The humeral component typically includes an elongated stem that is implanted into the intramedullary canal of the patient's humerus. In such a total shoulder replacement procedure, the natural glenoid surface of the scapula is resurfaced or otherwise replaced with a glenoid component that provides a bearing surface upon which the prosthetic head of the humeral component articulates.
As alluded to above, the need for a shoulder replacement procedure may be created by the presence of any one of a number of conditions. One such condition is the deterioration of the patient's scapula in the area proximate to the glenoid surface as a result of, for example, glenohumeral arthritis. In such a condition, the erosion of the patient's scapula is generally observed posteriorly on the glenoid surface. Such erosion of the scapula renders treatment difficult, if not impossible, with a conventional glenoid component. One way to treat such a condition is by the use of a modified glenoid component, known generally as an augmented glenoid component. An augmented glenoid component has a posterior edge that is thicker than the corresponding anterior edge.
From time-to-time, revision surgery is performed to replace a glenoid component. In such a revision surgery, the previously implanted glenoid component is surgically removed and a replacement glenoid component is implanted in the patient's glenoid. The subcondylar plate may be damaged or missing subsequent to revision surgery. Revision surgery may also result in defects, some of which may be fairly large, in the cancellous bone of the glenoid vault of the scapula. Fixation of a revision glenoid component can be difficult to achieve with the limited bone remaining on the glenoid vault of the scapula after the revision surgery has been performed. Vault-filling revision glenoid components have been developed that include a metal backing that extends into (i.e., “fills”) the glenoid vault to replace the lost bone. A bearing component, generally made of polyethylene (e.g., UHMWPE) or other materials such as ceramics or metals, is then fixed to the implanted metal backing to create the bearing surface upon which the proximal end (e.g., a prosthetic head) of the humeral component articulates.
Simple surgical instruments such as revolving spherical or circular reamers are generally used to prepare the glenoid surface during a glenoid surgical procedure. This is sufficient since traditional glenoid components (i.e., non-augmented glenoid components or non-vault-filling glenoid components) typically have a uniform backside geometry that is either curved or flat, which makes glenoid preparation fairly straightforward. However, the use of glenoid components with complex backside geometries (e.g., augmented glenoid components or vault-filling glenoid components) makes bone preparation more of a challenge. A surgeon is forced to use a combination of reamers, saws, and burrs in the performance of a free-hand technique that requires frequent interruptions for intraoperative assessment to implant these complex components.
A similar condition can occur in the acetabulum of a patient's hip. Namely, deterioration of the patient's hip bone in the area proximate to the acetabulum can occur as a result of, for example, arthritis. Such erosion of the hip bone renders treatment difficult, if not impossible, with a conventional acetabular component. One way to treat such a condition is by the use of an acetabular augment component that replaces the diseased or damage bone tissue.